Activity with pH

164 using an ox-spleen preparation, was the first to observe that the pH-activity curve has two peaks, and that they show little shift in pH 

0 Phosphate-citrate buffer.b Phosphate-acetate buffer. High or low mouse strains (see Section II). Phthalate buffer. Veronal-acetate buffer. 

Mammalian /3-glucuronidase shows a shift in optimum toward a more alkaline pH in the presence of certain anions, such as deoxyribonucleate (see Fig. 4) and phthalate,8 49 8 MW 169 and the optimum at about pH 5.2 becomes predominant over whatever peak or peaks the pH-activity curve may previously have displayed (see Section IX, 2). Certain heavy-metal ions in trace amounts cause a shift in the optimum toward a more acid pH 

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Fig 1 Comparison of Chlorine Dioxide Pre-cursor Activation with pH (after 5 min)... 

From studies of the variation of enzymic activity with pH, the ionization constants of groups believed to be at the active centers of the alpha-amylases have been calculated, as shown in Table XII. 

Studies of the variation of enzymic activity with pH have indicated that a-amino and imidazolium groups are important entities in the potato phosphorylase molecule, and this evidence has been further substantiated by the results of photo-oxidation and acetylation experiments. Rabbit-muscle phosphorylase a has been modified by photo-oxidation and alkylation, and the effect of both procedures was markedly decreased by the presence of D-glucosyl phosphate or glycogen this result indicates that the amino acid residues affected are at, or near, the active center. These acids may be histidine and cysteine, but other interpretations of the results are possible. 

The variation in Na-K ATPase activity with pH and with Na K ratio is shown in Figures 3 and 4. Although some differences are apparent in the curves obtained with the various divalent cations, the qualitative behavior is the same for all. However, the relative activating effect is pH dependent. The patterns of activity variation in Figures 3 and 4 could be duplicated using controls that contained choline acetate instead of Na+-K+ acetate and ouabain, and so they do not reflect variations in degree of ouabain inhibition. No activating effect under the conditions studied could be found for Ba2+, Ca2+, Cd2+, Cu2+, Fe2+, Pb2+, or Sr2+. 

The uridine phosphorylase activities of animal tissues appears to be of two types, which can be distingui ed on the basis of their pH optima. Uridine-cleaving enzymes of the chicken, human, guinea pig, and frog have pH optima in the vicinity of 6.5, as does the enz rme from E. ccli. The tissues of the rat, mouse, and dog have uridine phosphorylase activities with pH optima about 8 (25). 

Direct Application Rock. Finely ground phosphate rock has had limited use as a direct-appHcation fertilizer for many years. There have been widely varying results. Direct appHcation of phosphate rock worldwide amounts to about 8% of total fertilizer phosphate used, primarily in the former Soviet Union, France, Brazil, Sri Lanka, Malaysia, and Indonesia. The agronomic effectiveness of an apatitic rock depends not only on the fineness of the grind but also strongly on the innate reactivity of the rock and the acidity of the sod performance is better on more acid sods. Probably more than half of the potentially productive tropical sods are acidic, some with pH as low as 3.5—4.5. Certain phosphate rocks may thus become increasingly important as fertilizer in those areas. The International Fertilizer Development Center at Muscle Shoals, Alabama is active in researching this field (30). 

PH-20, a guinea pig sperm protein of 64 kD, is present on both the plasma membrane and inner acrosomal membrane of sperm. It is essential for adhesion of sperm to the zona peUucida, the initial step in the fertilization process. Active immunization with PH-20 causes infertility in both male and female guinea pigs for a period ranging from 6 to 15 months (120). 

The working conditions of the immunosensor (enzyme and antigen concentrations, dilutions of the antibodies, pH of the buffer solution) were found. The cholinesterase immobilized demonstrated the maximum catalytic activity in phosphate buffer solution with pH 8.0. The analytical chai acteristics of the sensor - the interval of the working concentrations and detection limit - have been obtained. The proposed approach of immunoassay made possible to detect 5T0 mg/ml of the bacterial antigen. 

FIGURE 14.11 The pH activity profiles of four different enzymes. Trypsin, an intestinal protease, has a slightly alkaline pH optimnm, whereas pepsin, a gastric protease, acts in the acidic confines of the stomach and has a pH optimmn near 2. Papain, a protease found in papaya, is relatively insensitive to pHs between 4 and 8. Cholinesterase activity is pH-sensitive below pH 7 but not between pH 7 and 10. The cholinesterase pH activity profile suggests that an ionizable group with a pK near 6 is essential to its activity. Might it be a histidine residue within the active site ... 

In the case of the stainless steels, or other readily passivated metals, the rapid reduction of dissolved oxygen on the freely exposed surface will be sufficient to exceed the critical current density so that the metal will become passive with a potential greater than whereas the metal within the crevice will be active with a potential less than. The passivation of the freely exposed surface will be facilitated by the rise in pH resulting from oxygen reduction, whilst passivation within the crevice will be impeded by the high concentration of Cl ions (which increases the critical current density for passivation) and by the H ions (which increases the passivation potential E, see Section 1.4). 

Fig. 8.2 Gel filtration on a column of Sephadex G-100 at pH 8 (both panels) of the crude extract of Gonyaulax polyedra cells prepared at pH 8 (upper panel) and prepared at pH 6 (lower panel). The activities of the 35 kDa and 130 kDa luciferases are measured by the addition of an excess of luciferin at pH 6.3 ( ) or at pH 8(A). The activity of the luciferin-bound LBP (luciferin-binding protein) in the upper panel is measured after the addition of an excess of 35 kDa luciferase at pH 6.3 ( ). In the lower panel, the LBP activity can be obtained by the addition of an excess of luciferin at pH 8, followed by the removal of unbound luciferin with a small column of Sephadex G-25 before the luminescence assay of bound luciferin at pH 6.3 (see the Section 8.2.8). The Overlap in the upper panel is the light emission resulting from the mixing of an aliquot of the fractions with pH 6.3 buffer. From Fogel and Hastings, 1971, with permission from Elsevier.

Chlorhexidine base is not readily soluble in water therefore the freely soluble salts, acetate, gluconate and hydrochloride, are used in formulation. Chlorhexidine exhibits the greatest antibacterial activity at pH 7-8 where it exists exclusively as a di-cation. The cationic nature of the compound results in activity being reduced by anionic compounds including soap and many anions due to the formation of insoluble salts. Anions to be wary of include bicarbonate, borate, carbonate, chloride, citrate and phosphate with due attention being paid to the presence of hard water. Deionized or distilled water should preferably be used for dilution purposes. Reduction in activity will also occur in the presence of blood, pus and other organic matter. 

Activation studies were conducted at pH 7.5 at 30°C in 20 mL of 0.5% high methoxyl citrus pectin (Citrus Colloids, Hereford, U.K.). Final cation concentration in PE extracts used for activation studies was less than 2 mM as measured by potentiometry. Controls were conducted to correct for non-enzymic alkali consumption, with no polyamine/no PE and polyamine added/no PE. PE activity was normalized as a percentage of activity with no cation addition. 

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